Tribasodites pugiunculus, Yin, 2022

Yin, Zi-Wei, 2022, The Batrisini of Tibet: unveiling an enigmatic ant-loving beetle diversity at Earth’s “ Third Pole ” (Coleoptera, Staphylinidae, Pselaphinae), Zootaxa 5111 (1), pp. 1-211 : 168-171

Tribasodites pugiunculus sp. nov.

( Figs 72 , 86C , 89 , 92C )

Chinese common name: 匕ḇûḃà甲

Type material (18 exx.). HOLOTYPE: CHINA: ♂ , ‘ China: Xizang, Gyirong County, Gyirong Valley, pass nr. Jifu Vill. , 28°21’35”N, 85°20’46”E, 2600–2700 m, 19.vi.2021, Z. Peng, Z. Yin & W. Zhang leg., ƱẪU喀NJ吉P W吉ė村ṉữ山ě ’ ( SNUC) . PARATYPES: CHINA: 10 ♂♂, 6 ♀♀, same data as that of holotype; 1 ♂ , ‘ China: Xizang A. R., Nyalam County, Zhangmu Town, pass nr. Lixin Village (ca. 27°57’22”N, 85°58’34”E), 2600 m, 24.vii.2010, W.-X. Bi leg. [ƱẪỄŃ木县樟木WĒẾ村]’ (all paratypes in SNUC) .

Diagnosis. Male. Body length approximately 2.3–2.4 mm. Head sub-rectangular at base, approximately as wide as pronotum, tempus moderately short, rounded at posterolateral angle, vertex lacking sulcus, with relatively large, asetose foveae, with distinct mediobasal carina extending from head base anteriorly slightly beyond level of posterior margin of eyes, with distinct lateral carina from base to posterior margin of antennal tubercle; antenna elongate, with modified antennomeres 10–11, antennomere 11 with short basal projection. Pronotum with laterally carinate median and lateral longitudinal sulci, with pair of discal carinae, with two pairs of antebasal and distinct marginal spines. Discal stria of elytron long, extending posteriorly to more than apical 1/4 of elytral length; disc finely punctate. Mesotibia with large, blade-like apical projection. Aedeagus strongly asymmetric; median lobe with extended basal capsule and elongate foramen, ventral stalk broad at middle and then abruptly narrowing and protruding apically, dorsal lobe large, plate-like, with elongate sclerite narrowing towards apex. Female. Body length slightly over 2.2 mm, antenna shorter than male, antenna and legs lacking modifications, genitalia as in Fig. 72K .

Description. Male. Body ( Fig. 72A ) length 2.30–2.41 mm; color reddish-brown, tarsi and mouthparts lighter. Dorsal surface of body covered with relatively dense pubescence.

Head ( Fig. 72B ) sub-rectangular at base, much wider than long, length 0.45 mm, width across eyes 0.53–0.55 mm; vertex smooth, lacking sulcus, vertexal foveae (dorsal tentorial pits) asetose, relatively large, mediobasal carina distinct, extending from head base anteriorly to slightly beyond level of posterior margin of eyes, lateral carina distinct, extending from base to posterior margin of antennal tubercle; posterolateral margin rounded; frons weakly impressed between large, moderately raised antennal tubercles, anteriorly demarcated from clypeus by frontalclypeal ridge; clypeus with smooth surface, its entire anterior margin strongly carinate and moderately raised; ocular-mandibular carina complete, carina branched below eye, extended ventrally and then anteriorly to posteroventral articulation of mandible. Venter with smooth surface; small gular foveae (posterior tentorial pits) originating from shared oval opening, with thin median carina extending from opening anteriorly to mouthparts. Compound eyes prominent, composed of approximately 40–50 ommatidia. Antenna elongate, length 1.25–1.29 mm, distinct club ( Fig. 72C ) formed by enlarged apical three antennomeres; antennomere 1 thick, subcylindrical, 2–7 each slightly elongate, 8 smallest, moniliform, 9 much wider than 8, transverse, 10 ( Fig. 72D ) much broader and longer than 9, ventral surface occupied by large mesal impression, 11 largest, much longer than 9 and 10 combined, with short, subtriangular and slightly curved projection at base of mesal margin, base of projection with tiny semicircular tubercle.

Pronotum ( Fig. 72B ) slightly wider than long, length 0.53 mm, width 0.54–0.57 mm, widest at middle; lateral margins rounded and with small denticles at apical 1/2, convergent basally and parallel at basal 1/4; disc slightly convex, finely punctate, broad median longitudinal sulcus with carinate sides, posteriorly confluent with oval antebasal impression and short mediobasal carina, with pair of discal carinae and lateral longitudinal sulci; with two pairs of antebasal and distinct marginal spines; lateral antebasal foveae small and asetose; with small outer and inner pair of basolateral foveae. Prosternum with anterior part slightly longer than coxal part, with small lateral procoxal foveae; thick hypomeral ridge extending from base to middle of anterior part, with punctiform lateral antebasal hypomeral pit; margin of coxal cavity broadly carinate.

Elytra much wider than long, length 0.67–0.71 mm, width 0.83–0.85 mm; each elytron with three moderately large, asetose basal foveae; long discal stria extending posteriorly from outer basal fovea to more than apical 1/4 of elytral length; humerus denticulate, subhumeral fovea present, carinate marginal stria extending from fovea to posterior margin of elytron.

Mesoventrite short, demarcated from metaventrite by transverse carinae; median mesoventral foveae narrowly separated, originating from shared opening, large lateral mesoventral foveae not forked internally, with short mesoventral process, with complete marginal stria. Metaventrite prominent admesally, inclined towards middle, with well-developed lateral mesocoxal foveae, two lateral metaventral foveae moving medially and in large, setose shared impression; posterior margin roundly emarginate at middle, lacking split.

Legs elongate; procoxa with exceptionally long seta at base, protibia with small preapical denticle at mesal margin; mesotrochanter ( Fig. 72E ) with distinct ventral spine, mesotibia ( Fig. 72F ) with broad, blade-like projection before apex; metatrochanter ( Fig. 72G ) with long ventral projection slightly to strongly curved at apex, metatibia with long pencil-like apical tuft of setae.

Abdomen widest at lateral margins of tergite 1 (IV), length 0.72–0.74 mm, width 0.74–0.78 mm. Tergite 1 (IV) more than twice as long as 2 (V), lacking basal sulcus, with large mediobasal and one pair of basolateral foveae, with pair of short discal carinae, marginal carinae complete, oblique inner carina thinner than outer one; tergite 2 (V) slightly longer than 3 (VI), 4 (VII) shorter than tergites 2 and 3 combined; tergites 2–4 (V–VII) each with one pair of basolateral foveae, tergite 5 (VIII) semicircular, transverse, posterior margin roundly emarginate at middle. Sternite 2 (IV) with one pair of mediobasal and two pairs of basolateral foveae, with long, oblique lateral carina; midlength of sternites 2–4 (IV–VI) gradually shorter, 5 (VII) slightly longer than 4, 3–5 each with two pairs of small basolateral foveae and short lateral carinae, sternite 6 (VIII) transverse, posterior margin broadly emarginate, sternite 7 (IX) ( Fig. 72H ) weakly sclerotized, slightly oval.

Aedeagus ( Fig. 72I, J ) 0.42–0.50 mm long, strongly asymmetric, elongate; median lobe with large extended basal capsule and elongate foramen, ventral stalk in dorsal view broad at middle and abruptly narrowing apically, with expanded, weakly sclerotized apex; dorsal lobe large, plate-like, apical part protruding and curved, narrowing towards apex; parameres membranous, apically split into two lobes.

Female. Similar to male in external morphology; antenna approximately as long as that of male; antenna and legs lacking modifications; each compound eye composed of approximately 50 ommatidia. Measurements (as for male): body length 2.23–2.30 mm; length/width of head 0.43–0.44/ 0.53–0.55 mm, pronotum 0.50–0.51/ 0.54 mm, elytra 0.63–0.66/ 0.81–0.83 mm; abdomen 0.74/ 0.74–0.75 mm; length of antenna 1.12–1.27 mm; genitalia weakly sclerotized ( Fig. 72K ), maximum width 0.32 mm.

Comparative notes. Tribasodites pugiunculus belongs to the group of species centered on T. antennalis which share similar locations of the male antennal modifications and general form of the aedeagus. The male of T. pugiunculus can be separated from the other species by the large blade-like projections near the apices of the mesotibia, where both T. antennalis and T. bari possess much smaller spines at the same position. Tribasodites pugiunculus further differs from both species by the short, apically narrowed basal projections of antennomeres 11, while the projections are much larger and broader in T. antennalis and much more greatly prolonged for in T. bari . The distinctive form of the aedeagus also leads to a confident identification of T. pugiunculus .

Distribution. Gyirong and Nyalam County, Tibet, SW China ( Figs 86C , 89 , 92C ).

Etymology. The new species epithet ‘ pugiunculus (a small dagger)’ is a Latin noun referring to the blade-like apical projections on the male mesotibiae.

Remarks. Parasitic Laboulbeniales were found on tergites 2 and 3 (IV and V) of the Nyalam specimen.

Figures

FIGURE 72. Morphology of Tribasodites pugiunculus sp. nov. (A–J. Male. K. Female). A. Dorsal habitus. B. Head and pronotum. C. Antennomeres 9–11. D. Antennomere 10, ventral. E. Mesotrochanter. F. Apical part of mesotibia. G. Metatrochanter. H. Sternite 7 (IX). I, J. Aedeagus, lateral (I) and ventral (J). K. Genitalia. Scale bars: 0.5 mm in A; 0.3 mm in B; 0.2 mm in C, I, J; 0.1 mm in D–H, K.

FIGURE 86. Distribution of Tibetan Batrisini. A. Tribasodites dilophus sp. nov. (circle), T. elongatus sp. nov. (triangle) and T. grandiceps sp. nov. (square). B. T. gyirong sp. nov. (circle), T. kiypu sp. nov. (triangle) and T. mirabilis sp. nov. (square). C. T. prolixicornis sp. nov. (circle), T. Tribasodites pugiunculus sp. nov. (triangle) T. vertexalis sp. nov. (square) and T. yatung sp. nov. (diamond).

FIGURE 89. Environment of and collecting sites at Gyirong Valley. A. General environment of the valley. B–E. Forests (B, E) and collecting sites (C, D) in the valley. D. A sign of Kiypu Village (吉ė村), which is the entrance to the forest. Photo Credit: A by Wen-Xuan Zhang.

FIGURE 92. Environment of Zhangmu Valley (樟木沟). Environment of Youyiqiao (友谊桥) (A, B), Lixin Village (ĒẾ村) (C) and Qu Township (DZ乡) (D). Photo Credit: A, B by Jian-Qing Zhu; C, D by Wen-Xuan Bi.